1. Field of Invention
The present invention relates to a media receiving apparatus, a media system comprising the media receiving apparatus, and control methods thereof. More particularly, the present invention relates to a media receiving apparatus which receives and processes a media signal which is copy-protected, a media system comprising the media receiving apparatus, and control methods of the media receiving apparatus and the media system.
2. Description of the Related Art
A transmission interface for a media signal uses a Digital Visual Interface (DVI) and/or a High Definition Multimedia Interface (HDMI). The DVI and the HDMI are used as an interface for a digital signal using Transmission Minimized Differential Signaling (TMDS) link technology.
FIG. 1 is a block diagram of a media system which uses a conventional HDMI interface. As shown in FIG. 1, a media source 10 which transmits a media signal for the HDMI interface, includes a TMDS transmitter 11. A media receiving apparatus 20 which receives the media signal includes a TMDS receiver 21 and an Extended Display Identification Data (EDID) read-only memory (ROM) 23.
The TMDS transmitter 11 modulates a digital media signal which is a combination of a video signal and an audio signal to a high-speed serial data. The TMDS receiver 21 receives and demodulates the modulated signal.
Techniques for protecting high-definition digital contents are gaining popularity. Therefore, a High-bandwidth Digital Content Protection (HDCP) protocol has been suggested as a specification prevent the copying of digital content in DVI and HDMI environments.
The HDCP protocol relates to a technique for encoding and decoding digital content between the media source such as personal computers (PCs), digital versatile disk (DVD) players and set-top boxes, and the media receiving apparatus such as monitors, televisions, and projectors. The HDCP protocol specifies that the transmitting side performs a certain authentication process for the receiving side with respect to digital content requiring protection so that only authenticated devices can display or output the content.
The authentication process between the media source 10 and the media receiving apparatus 20 according to the HDCP is now explained with reference to FIGS. 1, 2 and 3. FIG. 2 is a flowchart explaining the HDCP operation and FIG. 3 is a screen showing the HDCP operation of the conventional media system, which is analyzed by analysis equipment.
First, the media source 10 verifies whether it is connected to the media receiving apparatus 20 through a Hot Plug Detect (HPD) pin (S10). “2. Hot Plug PASS” in FIG. 3 indicates the result of the connection verification.
When the TMDS transmitter 11 confirms the connection to the media receiving apparatus 20 through the HPD pin, the media source 10 reads out EDID information stored in the EDID ROM 23 of the media receiving apparatus 20 through a Display Data Channel (DDC) line (S11). The media source 10 sets a resolution and an output specification of the media signal according to the read EDID information.
The TMDS transmitter 11 performs an initial authentication with the TMDS receiver 21 (S12). The analysis result of the HDCP initial authentication is shown on the left in FIG. 3. The initial authentication is performed in a manner to allow a Secrete Device Key and a Key Selection Vector (KSV) assigned from the Digital Current Protection LLC to be mutually exchanged between the TMDS transmitter 11 and the TMDS receiver 21, thereby generating Link Integrity data (R1) required for the authentication by the transmitter 11 and the receiver 21. R1 is data required for the authentication. The TMDS transmitter 11 determines whether the authentication is successful by comparing its generated authentication data (R1) and the authentication data of the TMDS receiver 21 (S13).
If the initial authentication is successful, the connectivity of the HDMI interface is periodically verified (S14). An analysis result of the verification of the HDCP connectivity is shown on the right in FIG. 3.
Examination occurs in periods of 128 frames (2 seconds) to determine whether the HDCP is normally performed while the HDMI line is normally connected. The authentication data (R1) is updated based on control CTL data which is input through a TMDS channel, and the authentication data (R1) has an index A to verify the same corresponding values at the same time instance. The TMDS transmitter 11 reads out the authentication data from the TMDS receiver 21, compares it with its computed authentication data, and thus determines whether the authentication is successful (S15).
If the authentication is successful, the transmitting side outputs a normal media signal decodable at the receiving side, and the receiving side normally decodes the media signal (S16). Next, the receiving side can display the decoded signal. If the authentication is unsuccessful, the transmitting side scrambles the screen or sets the screen to mute at the receiving side by force (S17).
Meanwhile, HDCP authentication error may occur due to various factors even in a normal environment. For example, the connection state of a connector may become temporarily poor due to shock during the normal operation, or the communication may fail due to noise incurred at power supply. As indicated by B, and in contrast to A, in FIG. 3, when the authentication data (R1) do not match, it is impossible to view a normal screen with audio because of the authentication failure. In this case, the normal operation can be performed by restoring the HDMI line as indicated by C.
According to the HDCP specification, if the HDCP authentication fails, the TMDS transmitter 11 can set the video signal and/or audio signal to mute. At this time, the index does not increase. When the index does not increase, both the media source and the media receiving apparatus should not increase the index together. If the media source increases the index after mute setting while the media receiving apparatus does not increase its index, the index values will not match. Additionally, a temporal difference from the mute setting to the non-increase of the index is crucial. In conclusion, when the mute is set, the media source and the media receiving apparatus are highly likely to hold different index values. In this situation, even when the HDMI line is restored, the normal screen is not displayed because of the different index values.
Generally, there is no serious problem when the connectivity is verified based on the index value every 2 seconds (128 frames) at a minimum after the success of the initial authentication. However, once the index values do not match, it is meaningless to compare the authentication values through the connectivity verification. At this time, the media source 10 should match the index values by recommencing the authentication from the beginning.
Mostly, the media source 10 is responsible for the control in relation to the HDCP, and the media receiving apparatus 20 serves merely passive functions to reply by updating the relevant data upon the request from the media source 10. Therefore, it is impossible to view the normal video with audio unless the media source 10 resolves this problem. As a result, a user is inconvenienced when the user disconnects and re-connects the HDMI line, or turns off/on the system for the sake of normal viewing.
Accordingly, there is a need for an improved system and method for resolving errors by determining an authentication error which occurs in relation to the copy protection and for providing an authentication error signal.